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Vulnerability record · CVE-2026-86439 · published 7 September 2026

CVE-2026-86439: Path traversal vulnerability

knowns versions before 0.30.0 fail to validate filesystem paths in MCP tool arguments, allowing attackers to read, create, overwrite and delete files outside the project directory. Attackers can supply path arguments containing directory traversal sequences to access arbitrary Markdown files accessible to the server process.

8.7 CVSS 4.0 High EPSS 1.1% · top 36.3% CWE-22 · Path traversal Deferred
8.7CVSS 4.0 base score
1.1%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
6References
8 Sep 2026Last modified by NVD

Description

knowns versions before 0.30.0 fail to validate filesystem paths in MCP tool arguments, allowing attackers to read, create, overwrite and delete files outside the project directory. Attackers can supply path arguments containing directory traversal sequences to access arbitrary Markdown files accessible to the server process.

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

References

LinkTags
https://github.com/knowns-dev/knowns/blob/v0.29.1/internal/storage/doc_store.go#L124-L129
https://github.com/knowns-dev/knowns/blob/v0.29.1/internal/storage/memory_store.go#L203-L211
https://github.com/knowns-dev/knowns/commit/09c5a96fd5817b941dc86669278c1a17db10ed4e
https://github.com/knowns-dev/knowns/releases/tag/v0.30.0
https://github.com/knowns-dev/knowns/security/advisories/GHSA-9gfj-28hw-jchp
https://www.vulncheck.com/advisories/knowns-before-0.30.0-path-traversal-via-mcp-doc-and-memory-tools

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Source: NIST National Vulnerability Database (record CVE-2026-86439), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.